1. Field of the Invention
The present invention relates generally to a vibration damping device to be used, for example, for automotive engine mounts, body mounts, member mounts and the like, and more particularly, to a fluid-filled vibration damping device utilizing vibration damping effects based on the flow behavior of a fluid sealed therein.
2. Description of the Related Art
Conventionally, there has been known a fluid-filled vibration damping device as a vibration damping connecting body or a vibration damping supporting body interposed between the members constituting a vibration transmission system. The vibration damping device has a structure where a first mounting member and a second mounting member mounted to each member constituting the vibration transmission system are elastically connected by a main rubber elastic body. Also, the fluid-filled vibration damping device that utilizes the flow behavior of a fluid has been known as a vibration damping device. This fluid-filled vibration damping device has a structure where a pressure-receiving chamber and an equilibrium chamber are formed on either side of a partition member supported by the second mounting member and are filled with a non-compressible fluid sealed therein, and further, an orifice passage is formed to connect the pressure-receiving chamber and the equilibrium chamber with each other. For example, the one disclosed in Japanese Unexamined Patent Publication No. JP-A-2009-243510 is such a device.
Using the fluid-filled vibration damping device, a vibration damping effect is effectively obtained against vibration of frequency to which the orifice passage is tuned based on the flow behavior of the fluid, while such an effective vibration damping effect can hardly be obtained against vibration of frequencies outside the tuning frequency. Especially since the orifice passage is substantially shut off due to antiresonance when vibration with a frequency higher than the tuning frequency is inputted, a problem of degraded performance of vibration damping arises due to an increased dynamic spring constant.
For that reason, the structure described in JP-A-2009-243510 is proposed with a liquid-pressure transmission mechanism provided with a fluid passage that allows the liquid pressure to be transmitted between the pressure-receiving chamber and the equilibrium chamber when vibration with a frequency higher than the tuning frequency of the orifice passage is inputted. This liquid-pressure transmission mechanism has a specific structure where a movable member (movable plate) is housed in a housing space formed in the partition member, and the liquid pressures of the pressure-receiving chamber and the equilibrium chamber are each applied to either side of the movable member via the communication holes formed through the wall of the housing space. Then, during input of a high-frequency, small-amplitude vibration, the movable member undergoes a slight displacement or deformation to allow the liquid pressure to be transmitted between the pressure-receiving chamber and the equilibrium chamber, while during input of a vibration in the range of the tuning frequency of the orifice passage, the movable member shuts off the communication holes to prevent the liquid pressure from being transmitted between the pressure-receiving chamber and the equilibrium chamber. This makes it possible to obtain, selectively and effectively in each case, a vibration damping effect exerted by fluid flow through the orifice passage as well as a vibration damping effect exerted based on the liquid-pressure absorption action of the liquid pressure transmission mechanism.
However, in the fluid-filled vibration damping device provided with the liquid-pressure transmission mechanism described above, the striking noise generated by impact forces tends to become a problem when the movable member comes in contact with the inner face of the housing space. In other words, there is a risk of abnormal noise generated in the vehicular body by delivering the impact energy of the movable member coming into contact with the inner face of the housing space to the vehicular body via the partition member and the second mounting member in support thereof.
In addition, during input of vibration with even a higher frequency than the resonance frequency of the fluid flowing through the fluid flow channel, there was a problem of significantly degraded vibration damping performance caused by a rapidly increased dynamic spring constant, since not only the orifice passage but also the fluid flow channel is substantially shut off due to antiresonance.